Most homes today are wired with NM-B cable, better known by the brand name Romex. It is the standard for residential branch circuits because it is affordable, flexible, and straightforward to install inside walls and ceilings. Knowing what your home is wired with, and how modern wiring is color-coded, helps you understand your electrical system and spot when something is outdated.
Here is what wiring most homes use today and how it works.
NM-B cable is the standard
NM-B stands for nonmetallic sheathed cable. It contains insulated copper conductors, a hot and a neutral, plus a bare copper ground, all wrapped in a plastic outer sheath. That sheath is why it is called nonmetallic, and it is what makes the cable easy to run through the framing of a house.
NM-B is designed for dry, protected indoor locations, such as inside walls, ceilings, and floors. It is the workhorse of modern residential wiring.
Modern wiring is color-coded
One helpful feature of modern NM-B cable is that the outer sheath is color-coded by wire size, which corresponds to the circuit it is meant for:
| Sheath color | Wire size | Typical circuit |
|---|---|---|
| White | 14 AWG | 15-amp circuits, lights and general outlets |
| Yellow | 12 AWG | 20-amp circuits, kitchens, some appliances |
| Orange | 10 AWG | 30-amp circuits, larger loads |
| Black | 8 AWG and larger | Higher-amp circuits |
| Gray | Underground feeder (UF) | Direct-burial and outdoor runs |
This color coding has been standard since the early 2000s, so if your home’s cable follows it, that points to relatively modern wiring.
Other wiring methods you may see
While NM-B dominates, a few other methods are common in specific situations:
- Individual conductors in conduit. In some regions and in exposed or wet areas like garages and basements, wires such as THHN are run inside metal or plastic conduit for added protection.
- Metal-clad (MC) or armored cable. These have a metal jacket for extra physical protection and are used where more durability is needed.
- UF cable. Underground feeder cable is used for outdoor and direct-burial runs, such as to a shed or detached garage.
Copper is the standard conductor for branch circuits. Aluminum is still used for some large feeders and service entrance conductors, but modern branch wiring is copper.
What older homes may have instead
If your home is older and has never been rewired, you may find outdated wiring rather than modern NM-B, such as knob-and-tube, cloth or rubber-insulated wiring, or aluminum branch wiring from the late 1960s and early 1970s. These older types can carry risks and are often reasons homeowners consider rewiring. An electrician can identify what you have during an inspection.
Most homes today use NM-B cable, commonly called Romex, which combines copper conductors and a ground in a plastic sheath and is color-coded by wire size: white for 14 gauge, yellow for 12 gauge, and orange for 10 gauge. Conduit, metal-clad cable, and UF cable serve specific situations. If your home has older wiring instead, it may be worth having an electrician evaluate whether an update is warranted.
Stella Electric rewires homes and updates outdated wiring for homeowners across the Baltimore area and throughout Maryland, with flat-rate pricing and no overtime charges. If you want to know what your home is wired with and whether it is due for an update, we can help. Financing is available on qualifying projects.
